(1) Field of the Invention
This invention relates to a method for applying electron beam curing high build coating and the coating composition therefor. More particularly, the invention relates to a method and composition for forming high build coating films such as multicolor finish, sand texture finish, rugged surface finish, multilayer finish, mastic finish and flock finish, which coating film are cured by applying electron beams, ultraviolet rays or the like.
(2) Description of the Prior Art
The coating materials of this kind are generally applied thickly (about 300 microns or more) and subjected to forced drying in every coating process. It is well known however, that several defects of the coating films such as checking, cracking, shrinking and popping are liable to occur when these high build coating are rapidly heated. As the method for eliminating these disadvantages, the curing of coating films by applying electron beams or ultraviolet rays has been proposed, but it is difficult to apply ordinary electron beams into the depth more than 300 microns of coating films, and much less when aggregates are contained in coating films. That is, electron beams cannot reach behind the aggregates as the beams are shaded by the aggregates and the coating material behind the aggregates cannot be cured. This tendency may be said of the use of ultraviolet rays. As a result, the durability of coating film becomes poor.
Further, several unsaturated resin coating compositions of radiation curing type have been proposed, however, the volumetric shrinkage is large if they are cured in a short time, and as a result, the adhesion of them to iron and other metal surfaces is not good. Furthermore, in connection with the insufficient curing of coating material in the shade portion during the curing with ionizing radiation, urethane type coating materials are thought of, however, the pot life of them are usually less than about 5 hours or so, while in the case that the pot life of such coating material is intended to prolong, the curing property in the initial stage becomes worse. As a result the conventional coating compositions have been restricted by several points in practical uses.